Most oilwells produce both hydrocarbons and water. The oilwell production fluid is usually highly corrosive. This is especially so in waterflood oilfields. Sometimes the corrosion problems are so great that a workover rig must pull the oilwell pumping unit and replace the pump and sucker rods every few weeks. This is quite expensive and unless a substantial production of hydrocarbons is realized from the well, the economics of many wells in a waterflood region becomes questionable, unless the problem of corrosion can be economically reconciled.
In many regions, it is popular to partially combat downhole well corrosion by introducing a treatment chemical, such as an inhibitor, into the annulus of the wellbore. The treatment chemical usually is admixed with water and pumped into the casing annulus at a rate of perhaps one treatment per week. This batch, or truck type, treatment provides an immediate high concentration of inhibitor in the wellbore, but the effectiveness of the treatment chemical rapidly tapers off until there is insignificant treatment available during the last few days of the cyclic treating time period.
Others have continually introduced treatment chemicals into the annulus, but this expedient does not always satisfactorily control the corrosion problem downhole in the borehole for the reason that the chemical preferentially migrates into the upper fluid column of the annulus where it remains in the hydrocarbon phase and therefore does not properly treat all of the metal components of the lower borehole.
The above prior art treatments generally require an excessive amount of inhibitor chemical which hardly ever is ideally placed in the proper area of the borehole to enable satisfactory protection from corrosion to be achieved.
It would be desirable to introduce a continuous stream of proper and effective treatment chemical into the annulus of a borehole, and to cause the treatment chemical to migrate down through the upper phase of the annular fluid and downhole to the casing perforations, where the treatment chemical becomes comingled with the production fluid and is returned up the tubing string to the surface of the earth, thereby properly coating all of the downhole metal components with the optimum amount of inhibitor required to control the downhole corrosion problems. Process and apparatus which obtains this desirable goal is the subject of the present invention.
______________________________________ Rodger, et al 2,688,368 Hampton 3,223,167 Rohrback 2,801,697 Bansbach 3,710,867 McNamra 2,843,206 Harrison 4,132,268 Marken 2,884,067 ______________________________________
The above references show that continuous downhole treatment of a wellbore is old, and that some of the produced fluid admixed with treatment chemical can be continuously circulated back to the well. The prior art fails to suggest the concept of using a specific flow rate of separated water admixed with a specific quantity of treatment chemical to achieve propagation of the mixture down through the annular fluid column to the bottom of the borehole, nor does the prior art suggest apparatus for carrying out this concept.